1. Field of the Invention
The present invention relates to a liquid ejection head and an image forming apparatus, and more particularly, to a liquid ejection head and an image forming apparatus in which a plurality of pressure chambers connected to a plurality of nozzles from which liquid is ejected are arranged in a two-dimensional configuration.
2. Description of the Related Art
In print heads (also called simply “heads”) mounted in image forming apparatuses, a so-called piezoelectric inkjet head is known, and for example, Japanese Patent Application Publication No. 9-314833, Japanese Patent Application Publication No. 2003-127366, Japanese Patent Application Publication No. 2001-179973, and Japanese Patent Application Publication No. 2004-1550 disclose such piezoelectric inkjet heads. In such a piezoelectric inkjet head, ink accommodated inside pressure chambers is pressurized by using the displacement of piezoelectric elements, ink droplets are ejected from nozzles connected to the pressure chambers, and thereby an image is formed on a recording medium.
Japanese Patent Application Publication No. 9-314833 discloses a head in which piezoelectric elements are arranged on a diaphragm which forms one wall of each pressure chamber. In this head, a reservoir is provided on the piezoelectric element side of the diaphragm, and ink is supplied from the reservoir to the pressure chambers via supply ports formed so as to pass through the piezoelectric elements and the diaphragm.
Japanese Patent Application Publication No. 2003-127366 discloses a head in which a space is provided in order to prevent the movement of piezoelectric elements formed on a diaphragm and a sealing substrate is provided for sealing the space. The reservoir is formed so as to pass through the diaphragm in a part outside the region of the row of pressure chambers, in such a manner that ink is supplied from the lower side of the pressure chambers.
Japanese Patent Application Publication No. 2001-179973 discloses a head having a structure in which the partitions of an ink supply tank provided on the piezoelectric element side of a diaphragm seal off the piezoelectric elements. In this head, ink is supplied to the pressure chambers from an ink supply tank, via ink supply channels formed in the diaphragm in regions other than the regions corresponding to the pressure chambers.
Japanese Patent Application Publication No. 2004-1550 discloses a head composed by stacking up a pressure chamber substrate in which pressure chambers are formed, a common electrode film having piezoelectric elements formed respectively at positions corresponding to pressure chambers, and a reservoir member having a lid-shaped structure which encloses a plurality of piezoelectric elements therein.
In recent years, there have been increasing demands for improved image quality and higher printing speeds, in inkjet heads. In order to meet these demands, it is necessary to form heads to higher density, and to enable them to eject high-viscosity ink at a high frequency.
However, in a head formed to high density, the ink flow channels tend to become highly complicated. As a result, the flow path resistance to the ink inside the head can increase, refilling characteristics can be degraded, it is difficult to eject high-viscosity ink at a high frequency, and consequently ink ejection becomes instable.
Furthermore, as the density of the head increases, the space for the electrical wires (internal wires) for driving the piezoelectric elements becomes insufficient, and the difficulty of wiring increases.
In the head disclosed in Japanese Patent Application Publication No. 9-314833, thin-film transistor elements (TFT) of equal number to the piezoelectric elements are arranged on a side face of the head, and wires from the TFTs are extended to, and connected to, drive electrodes of the piezoelectric elements. However, no consideration is given to a composition in which the piezoelectric elements are arranged in a two-dimensional configuration and the composition is not suitable for installation of high-density wiring.
In the head disclosed in Japanese Patent Application Publication No. 2003-127366, electrode wires which are connected electrically to a common electrode which is common for a plurality of piezoelectric elements are provided on a sealing substrate, and connecting sections for connecting these electrode wires with drive circuits for driving the piezoelectric elements are provided on the sealing substrate. However, the description only relates to a composition with one row of piezoelectric elements, and therefore, similarly to Japanese Patent Application Publication No. 9-314833, it is not suitable for installation of high-density wiring. Moreover, if the head disclosed in Japanese Patent Application Publication No. 2003-127366 is formed to a high density, then the ink flow channels become complicated, and there is a possibility that the refilling characteristics decline.
In the head disclosed in Japanese Patent Application Publication No. 2001-179973, electrical wires (internal wires) extended from the electrodes of the piezoelectric elements to the end section of the head are disposed in the same plane as the diaphragm on which the piezoelectric elements are disposed, and hence there is a high possibility that problems occur in the electrical wires, and the composition is therefore unsuitable for achieving high density in the head. Furthermore, the ink flow channels are composed by a plurality of bending channels, thus causing the refilling characteristics to decline, and making it difficult to eject high-viscosity ink at a high frequency.
In Japanese Patent Application Publication No. 2004-1550, there is no discussion of the method of installing the electrical wires (internal wires) for driving the piezoelectric elements, and there is a possibility that the above-described problems occur in these electrical wires.